Cobalt chloride, cyclization reactions

Beccalli et al. reported a new synthesis of staurosporinone (293) from 3-cyano-3-(lH-indol-3-yl)-2-oxo propionic acid ethyl ester (1464) (790). The reaction of 1464 with ethyl chlorocarbonate and triethylamine afforded the compound 1465, which, on treatment with dimethylamine, led to the corresponding hydroxy derivative 1466. The triflate 1467 was prepared from 1466 by reaction with trifluoromethanesulfonic anhydride (Tf20) in the presence of ethyldiisopropylamine. The palladium(O)-catalyzed cross-coupling of the triflate 1467 with the 3-(tributylstannyl)indole 1468 afforded the vinylindole 1469 in 89% yield. Deprotection of both nitrogen atoms with sodium ethoxide in ethanol to 1470, followed by photocyclization in the presence of iodine as the oxidizing agent provided the indolocarbazole 1471. Finally, reductive cyclization of 1471 with sodium borohydride-cobaltous chloride led to staurosporinone (293) in 40% yield (790) (Scheme 5.248). 

Other possible catalysts for the reaction of various alkyl bromides with allyhnagnesium hahdes in THF are cobaltbis(l,3-diphenylphosphino)propane complex (equation 70) or cobalt chloride in combination with a diamine (equation 71) °. Cyclization products can... 

Other transition-metal catalysts can be used for the alkylation of allylmagnesium halides with alkyl bromides such as cobalt 6 -(l,3-diphenylphosphino)propane complex Co(dppp)Cl2 (Scheme 2-34, eq. (a)) and cobalt chloride in combination with a diamine (Scheme 2-34, eq. (b)). Cyclization reactions are possible under these conditions. ... 

Other uses of cobalt(I) catalysts include the reductive intramolecular cyclization of bromocyclohexenones to form bicyclic ketones [391] and the radical cyclization of bro-moacetals [392,393]. Krautler and coworkers [394] found that 1,4-dibromobutane interacts with electrogenerated cob(I)alamin to afford a tetramethylene-l,4-di = Co -cobalamin species. In a recent study of the reactions of cobalt(I) tetraphenyl porphyrin with benzyl chloride or 1-chlorobutane, Zheng and coworkers [395] reported that alkyl radicals are transferred from the cobalt center to a nitrogen of a pyrrole ring, leading to formation of an A-alkyl cobalt porphyrin complex. 

For a few combinations of less reactive dienes and dienophiles, transition metal catalyzed variants of the Diels Alder reaction have been developed. An example is the cycloaddition of an unpolar diene and an unactivated alkyne however, except when the reaction is catalyzed with iron, nickel, cobalt, or rho-dium(I) complexes, the temperature required often causes competing decomposition, even for the intramolecular version. [2] Wilkinson s catalyst [3] - tris(triphenylphosphane)rho-dium(I) chloride - frequently used for hydrogenations and for decarbonylations, permits the cyclization of 4 to the annelated cyclo-hexadiene 5 in excellent yield in only 15 minutes at 55 °C in trifluoroethanol as solvent (Scheme 2). [2c]... 

The diene insertion reaction will take place intramolecularly if the diene system is part of the acyl group in the acylcobalt tetracarbonyl (13). Thus, /ra j-2,4-pentadienoyl(triphenylphosphine)cobalt tricarbonyl, prepared by the acid chloride method, cyclizes on heating in ether solution in a closed vessel at 75° C for an hour, to 7r-cyclopentenonyl(triphenylphosphine)cobalt dicarbonyl in 30% yield. 

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